The U.S. space agency NASA is set today to launch (19:00 Prague time) a space probe designed to test Albert Einstein's theories of relativity. According to one aspect of the famous theories, large objects such as planets, stars, and black holes distort time and space as they spin. Scientists say that if Einstein is correct, NASA's Gravity Probe B should be able to detect that a small bit of time and space are actually missing from the orbit of such large objects in space.

Prague, 20 April 2004 (RFE/RL) -- The great scientist Albert Einstein is not a man to be measured by ordinary means. The singular brilliance of his mind has left the world breathless since he evolved his famous theories of relativity in the early years of the 20th century.

Mere mortals, struggling to understand the theories, can at least appreciate the flashes of unconscious humor of the great man, as he sorted through his complicated formulations. For instance, he described an idea that struck him in 1907 as the "happiest thought" of his life -- namely, that a painter falling from the roof of a house would feel weightless when accelerating toward the ground. This clue led Einstein to reason that gravity and acceleration must be equivalent.

"You might ask why we need to test Einstein's theory, and I would say that fundamental science provides the underpinning of much of our modern science and technology, and the better we can measure and understand these effects, the better we can shape the world that we live in."

Upon this idea he based what he called the Equivalence Principle. But it's best not to prove the veracity of this idea first hand by climbing onto the roof of your house.

However, the U.S. space agency NASA is today set to start just such a practical test. It will send into space a $700 million probe that is designed to confirm -- for the first time in real terms -- one key aspect of the general relativity theories, relating to gravity.

Anne Kenney, the director of astronomy and physics at NASA headquarters, told a pre-launch briefing about the aims of the mission.

"Einstein predicts that space and time are both warped and dragged by the presence of our own massive and rotating Earth, and Gravity Probe B will test this prediction. Gravity Probe B studies very fundamental questions, and it does it in a very simple manner -- the simpler something is, the more difficult it is, and I would say that is the case with Gravity Probe B," Kenney said.

According to Einstein, large objects -- such as planets, stars, and black holes -- distort time and space as they spin. Scientists also want to check whether a big object like the Earth twists time and space into tornado-like rotations. If Einstein's theory is correct, scientists say the NASA probe should be able to detect that a small bit of time and space are actually missing from the orbit of such large objects in space.

A question that arises for nonscientists is whether it is appropriate to spend hundreds of millions of dollars on proving or disproving a very academic point. NASA's Kenney says it is worth it.

"You might ask why we need to test Einstein's theory, and I would say that fundamental science provides the underpinning of much of our modern science and technology, and the better we can measure and understand these effects, the better we can shape the world that we live in," Kenney said.

The probe is one of the most precise scientific instruments ever built. It consists of four nearly perfect spherical gyroscopes the size of pingpong balls. They are the roundest objects ever made, according to NASA, and they are what will carry out the measurements. The spheres are housed in a chamber that is the quietest ever produced, so sound waves will not affect them. They are suspended in liquid helium and chilled to almost absolute zero, so their own molecular activity will not jar them.

This delicate cargo will be shot into an Earth orbit of some 640 kilometers high from the rocket range at California's Vandenberg Air Force Base. Rex Geveden, the deputy director of NASA's Marshall Space Flight Center, gives some technical details of the experiment.

"The mission is divided conceptually into three different phases. The first phase is an initialization phase, which lasts about 60 days, and in that phase the instrumentation is activated, the guide star is acquired, the orbit is trimmed, the gyroscopes that are there suspended and spun up are [brought] in a line with the guide star. In other words, the experiment is made ready to do the measurement. That takes about two months. The second phase of the mission is called the science operation phase. This lasts about 13 months, to allow the sun conceptually to walk all the way around the space vehicle in the course of a year. And in this phase of the mission, the gyroscopes should be functioning normally, and this will be the science mode. The third phase is post-mission calibration. This is the final two months of the mission," Geveden said.

The idea of testing Einstein's theories in space in a practical way germinated at Stanford University in 1959, not long after the United States launched its first satellite. By 1964, NASA had agreed to take on the project. Today, 40 years later, it is reaching fruition.

As a leading figure in the project almost from the beginning, Stanford professor Francis Everitt welcomed the occasion.

"Well, this, of course, is a wonderful time for us at Stanford, and for our colleagues at NASA Marshall Center and NASA headquarters and also at Lockheed-Martin. It's great to be beyond the point of building to the point of actually launching," Everitt said.

Everitt says that -- despite the century that has passed since Einstein began expounding his theories -- still not enough is known about them, and the coming mission will help build a clearer picture of the world we live in.